Demagnetizer from transformer.

[olderdan]

Commercial versions of these can be quite expensive so here is a modified microwave transformer for demagnetising tools, there are more than one way do do this but the basic idea is to break the circuit of the laminated core and use the primary windings only.
The top of the core can be removed completely along with the secondary windings to create what is known as an E core and inverted to use the bottom face as the usable surface.
I have chosen to remove the secondary windings and make a saw cut though the top, I could have cut though the side but did not think of at the time, the cut is then filled with a non conducting material to prevent the ingress of anything that could bridge the gap, I did this because the mounting feet made it easier this way.
Mine has a working surface of 90 x 70 and work is passed along the direction of the laminations to demag, it is important to make a slow pass and continue until about a foot away before switching of.
A simple plywood box was made to the height of the core with a switch and warning light (the latter is not really necessary as it makes a rather loud buzzing noise when switched on).
A thin top cover is used to prevent marking of finished work and would ideally be made of fibre but not having any I used sturdy cardboard (those beer boxes again) which has been varnished.
I am sure this would overheat if left on but most things can be dealt with in under a minute.
This can demag quite large items and if I have a HSS tool that needs treatment I just draw the whole tool holder over it.
I have made a mini version for smaller items and this is often taken out to jobs outside the shop for drill bits etc.

[mklotz]

For those folks who may be intimidated by the idea of re-working a transformer...

At garage sales and swap meets keep your eye peeled for bulk tape erasers, a fixture in the days of reel-to-reel tape recorders. I've used one for years for small tools and it's worked very well. I don't do Ebay but that might be a possible source too.

[DIYer]

Thanks olderdan! We've added your Demagnetizer to our Miscellaneous category,
as well as to your builder page: olderdan's Homemade Tools. Your receipt:

Demagnetizer by olderdan

tags: demagnetizer

[Philip Davies]

I have dropped a box containing 100s of drill bits, used a magnet to pick them up, and now have to demagnetise the lot. How can I avoid electrocuting myself?

[mklotz]

I have dropped a box containing 100s of drill bits, used a magnet to pick them up, and now have to demagnetise the lot. How can I avoid electrocuting myself?

Do you have access to an old style bulk tape eraser?, e.g....

https://www.ebay.com/itm/30501168151...YAAOSwAqxkpc5f

If it were me, I would spread the drills in a thin layer on a flat, non-metallic surface and cover them with a sheet of thin plywood or corrugated cardboard. Then "iron" them with the eraser as one might iron clothes. The cover is to prevent them from attaching themselves to the eraser. Don't know if it would work but I'd try it. (I keep my drills in index holders so I'll not ever face this problem.)

Of course, no demagnetization is needed for wood drill bits or drills used on non-ferrous metals.

Another, less appealing, option is to demagnetize them one at a time as they come into use. Suggested methods here...

Demagnetizers

DIY Demagnetising tool that works

[Philip Davies]

A chore I must perform sometimes is to examine drill bits collected, reject the poorer sort and arrange them into sets. You can imagine that this is a very tedious task and inclines me to put it off!

[IntheGroove]

Why do dull drill bits become magnetized?

[hemmjo]

Why do dull drill bits become magnetized?

I believe it is from the heat generated and the vibrations of the cutting forces make the molecules in the steel align.

Hammering high iron content items can also magnetize them.

[Philip Davies]

However, in my case, I knocked a case of drill bits off the bench accidentally. Then I gathered them up with a magnet. So that’s two mistakes. The only way to get all the swarf off,was to polish them with a rotary fibre brush. At least they’re clean now, and ready for use, if not strictly in order, but they’re still magnetic. But I have frequently noticed drills retaining the swarf, so you’re probably right about the alignment. Thank you.